hausfather told us ac accounts for about 20% of electric use in homes that have it.here coal or natural gas used to make power, dr. zeke says more acs likely contribute to heating the planet. but in california, with so much solar power, the equation is different. >> when people get air-conditioning in california, a lot of the electricity being used to power that air-conditioning is going to be coming from solar panels, just because you tend to need air-conditioning when you have a lot of solar energy available. so that will help reduce the impact of more acs. >> if you decide to buy an ac, learn about seer when you're shopping, that's an acronym for seasonal energy efficiency ratio. each ac gets a seer number. the higher the seer, the less power it needs. caleb cameron is at the contractors state license board. he says beware of ac contractor who is demand a lot of money up-front. the law caps your down payment to 10% of cost of the job or $1,000, whichever is less. also, get your contract in writing, including a three-day right to cancel, which state law requires. >

zeke hausfather says you're right. let's look at berkeley.'70s the temperature only topped 85 degrees five days a year. today, it's hotter than 85 an average of 15 days each year. the rest of the bay area is pretty much in the same sweaty boat as berkeley. >> it used to be a very comfortable year-round temperature, we're increasingly moving into a climate where we have a couple weeks a year where it is unbearably hot to be in a home without air conditioning. >> reporter: homeowners responded. some local ac installers tell us sales are trending upward particularly in neighborhoods where people previously didn't need air conditioning. ♪♪ even in redwood city, where the famous old marquee boasts climate best by government test, permits to install new ac systems are generally climbing and hit a high in 2019. they did drop when the pandemic hit but ac sales are expected to rebound after covid-19 moves into the background. even dr. hausfather who lives in the east bay is looking to add a unit to his home. >> we're investing in getting a heat pump f

zeke hausfather: we're really seeing the signs of warming loud and clear in the data. female: our scienceappening to the redwood trees is a thinning forest, a more flammable forest. male: i think climate change has its fingerprints all over these types of fires. heather cooley: there are a lot of issues when we think about sea-level rise. failing to address these issues now is only gonna make it more expensive and more difficult. raj mathai: thanks for joining us for this nbc bay area special, "climate in crisis." it's been a year in which most of our journalistic work pointed toward the pandemic or the election or racial inequality, but we are not overlooking the health of our planet.